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I'm rebuilding the forks on my CB400 project bike [ turning into a street tracker ;) ]

The process from the manual is pretty straight forward:

1) Remove the front fork bolts and drain oil

2) With each fork bottom held in a vice, remove the socket bolt using the Allan key hand wrench and separate the pipe from the bottom case

3) Remove the front fork dust seal, 48mm snap ring and oil seal

One fork came apart no problems. I removed the bottom bolt which leads through and attaches to the oil lock piece, drained oil and slide the fork tube from the bottom case.

The other fork for some reason gets to a point when sliding out to separate the two pieces and it just 'clunks' and won't go any further. I've used a little force and nothing. It's like it is getting stuck on something / hitting something. From what I can see the oil lock piece is still in the bottom of the fork so it shouldn't be that. I can't think of anything else that would be obstructing it.

Any ideas of had this happen before?

Thanks in advance.

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Don't know about the CB400's fork in particular, but on some forks the bushings won't fit past eachother to allow easy removal of the stanchion ("pipe" 6 on diagram) from the slider ("case", 19 on diagram). Here's a partzilla diagram of a CB400F fork.

Partzilla part diagram

On some BMWs with SHOWA forks that I've worked on, the lower bushing (9, attached to pipe 6) won't fit through the installed upper bushing (8, pressed into the top of the case, 19).

The solution is force. remove the spring, then fully compress the pipe into the case, then rapidly pull the pipe out of the case. Repeat until upper bushing 8 is driven out of case 19. The pipe will then be separated from the case. This is often referred to as the slide hammer technique--you're using the pipe as a slide hammer to remove the upper bushing. The seal will come out too (don't forget to remove circlip 15)

Of course, since significant force is involved here, you want to be sure this procedure applies to your bike specifically. I'd ask around on some specialist CB forums. These bikes have a following, I'm sure you'll find your answer.

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  • Thanks for the information. Here is the diagram of the CB400/CB250 forks (same forks, from two different manuals). i.imgur.com/TqaDsb6.png & i.imgur.com/21sye0U.png I have the spring, rebound spring and fork piston out of the fork. So only the fork tube and oil lock piece should be left in there but it still won't budge. I slide out to around about where the groove on the fork tube meets the groove on the fork slider. So I think maybe something is getting stuck on the oil seal? I've tried a bit of brute on it but I'm concerned about the metal on metal clunking sound it produces
    – James
    May 18, 2013 at 6:28
  • I have to believe that the groove in the "pipe" is supposed to contain a bushing, and that there's another bushing pressed into the top of the slider. Neither of these are shown on the two diagrams you linked, but I don't see how the fork would work without them. You got the other side apart, were these bushings present?
    – mac
    May 20, 2013 at 14:46

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